Particles on Deforming Surfaces: Theory & Analysis

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Discussion Overview

The discussion revolves around the theoretical implications of a particle moving on a deforming surface, particularly in the context of analytical mechanics. Participants explore the validity of established principles such as the principle of virtual work and D'Alembert's principle when the surface is not static.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the applicability of the principle of virtual work and D'Alembert's principle when the normal force does work due to surface deformation.
  • Another participant asks for clarification on the specific force causing the deformation of the constraint, suggesting that understanding this force is crucial for analyzing the work done.
  • A different viewpoint suggests that the mathematical formulation can still be considered by treating the surface as a function of time that does not depend on the particle's motion.
  • One participant asserts that the D'Alembert-Lagrange principle remains valid under the conditions described, and references a specific text for further details.
  • A later reply acknowledges the referenced text as a valuable resource.

Areas of Agreement / Disagreement

Participants express differing views on the validity of established principles in the context of deforming surfaces, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

There are unresolved assumptions regarding the nature of the forces acting on the surface and the specific conditions under which the principles are applied. The discussion also highlights the dependence on definitions related to ideal constraints.

andresB
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All books in analytical mechanics explain the case of a particle moving on a given static surface. But what happen if, for example, the surface is having some deformation?. I imagine that the principle of virtual work, and hence, D'Alembert are no longer valid since the normal force by the surface do work. Hence Hamilton principle no longer work either.

is there a theory for a particle moving on such deforming surface?
 
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Can you specify the force is that is deforming the constraint? That is the source of the work.
 
FactChecker said:
Can you specify the force is that is deforming the constraint? That is the source of the work.

Well, It doesn't matter I think.

Mathematically, think in point moving along the surface S(x,y,z,t)=0, where the surface dependence on time is given beforehand and it is not affected by the motion of the particle.
 
Last edited:
By definition ideal constraints do not work on virtual displacements in your case ##\delta x,\delta y,\delta z,##
$$\frac{\partial S}{\partial x}\delta x+\frac{\partial S}{\partial y}\delta y+\frac{\partial S}{\partial z}\delta z=0$$
No problem, the D'Alembert-Lagrange principle keeps holding as well as all the Lagrangian formalism
For details see D T Greenwood Classical Dynamics
 
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wrobel said:
For details see D T Greenwood Classical Dynamics
That was a really good read, thank you.
 

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